[Haskell-cafe] List comprehension order of evaluation

Hi, Today, if I write: [a:[b] | a<-"ab" , b<-"12"] I get: ["a1","a2","b1","b2"] Are there any guarantees that I'll never get ["a1","b1","a2","b2"] instead, i.e., that the first list will always be the last one to be fully transversed? Even if I use a different compiler or a future version of Haskell? Reading how list comprehensions are translated in the Haskell report it seems the answer is yes. Is that written in stone? Can compilers do it in their own different way? Thanks, Maurício